1. Field of the Invention
The present invention relates to a non-resonant knocking sensor for detecting knocking vibration in an internal combustion engine and to a method for producing the non-resonant knocking sensor.
2. Description of the Related Art
A knocking sensor for detecting a knocking phenomenon is disposed in internal combustion engines of automobiles etc., and control is performed to suppress the generation of the knocking phenomenon according to the detection signal output from the knocking sensor. More specifically, delay angle control for changing the ignition timing of an ignition plug in an internal combustion engine is performed according to the output signal of the knocking sensor.
As the above-mentioned knocking sensor, those having various configurations have been proposed (for example, refer to JP 2003-322580A and JP 2006-112953A). Among the knocking sensors, a knocking sensor having a configuration shown in FIGS. 6 and 7 is known as disclosed in JP 2003-322580A. This knocking sensor 101 is installed in a cylinder block serving as one component constituting an internal combustion engine. It is a so-called center-hole-type non-resonant knocking sensor in which an installation hole 114 that is used when the knocking sensor 101 is installed in the cylinder block is formed at the central area thereof
As shown in the exploded view of FIG. 7, the knocking sensor 101 mainly has a metal shell 111 having a cylindrical section 112 and a flange section 113 formed at the lower end of the cylindrical section 112; and a lower insulating plate 116, a lower electrode plate 117, a piezoelectric element 119, an upper electrode plate 120, an upper insulating plate 122, a weight 123, and a belleville spring 124, each formed into an annular shape. The lower insulating plate 116, the lower electrode plate 117, the piezoelectric element 119, the upper electrode plate 120, the upper insulating plate 122, the weight 123, and the belleville spring 124 are fitted around the outer circumference of the cylindrical section 112 in this order from the side of the flange section 113.
At the radially outward end sections of the lower electrode plate 117 and the upper electrode plate 120, an upper terminal 121 and a lower terminal 118, from each of which a voltage is delivered, are provided so as to extend radially outward in a strip shape. An externally threaded section 115 is formed on the upper side of the outer circumferential surface of the cylindrical section 112. On the other hand, an internally threaded section 126 to be engaged with the externally threaded section 115 is formed on the inner surface of a nut 125. When the internally threaded section 126 of the nut 125 is threadedly engaged with the externally threaded section 115 of the cylindrical section 112, the nut 125 moves toward the flange section 113, and the stacked components ranging from the lower insulating plate 116 to the belleville spring 124 are pressed by the nut 125 toward the flange section 113 and fixed thereto (see FIG. 6).
The sensor body 110 configured as described above is covered with a resin molded body 140, to thereby form the knocking sensor 101. The knocking sensor 101 having this configuration is installed so that the lower surface of the flange section 113 of the metal shell 111 makes contact with the cylinder block and is used in this state.
3. Problems to be Solved by the Invention
In the knocking sensor 101 described in Patent Document 1 described above, when the internally threaded section 126 of the nut 125 is threadedly engaged with the externally threaded section 115 of the cylindrical section 112, there is a problem in that plated layers formed on the surfaces of the nut 125 and the cylindrical section 112 are peeled off and plating debris is likely to be generated. If such plating debris makes contact with the metal shell 111 and the lower electrode plate 117 or the metal shell 111 and the upper electrode plate 120, there is a danger that the knocking sensor 101 cannot output its detection signal accurately.
For the purpose of solving the above-mentioned problem, Patent Document 2 has disclosed a technology in which a cylindrical stopper ring is used instead of the nut 125 to press the stacked components ranging from the lower insulating plate to the weight toward the flange section. In this case, a groove section is formed on the outer circumferential surface of the cylindrical section of the metal shell facing the stopper ring, and the stopper ring is crimped onto the groove section, whereby the stopper ring is fixed to the cylindrical section.
With this configuration, the process of threadedly engaging the externally threaded section with the internally threaded section can be eliminated and the generation of plating debris caused by the thread engagement can be suppressed. Furthermore, two components, that is, the nut 125 and the belleville spring 124, for pressing the stacked components ranging from the lower insulating plate to the weight, can be replaced with one component, that is, the stopper ring. As a result, the number of components can be reduced.
However, in the knocking sensor described in Patent Document 2, there is a problem in that it is difficult to maintain insulation between the metal shell and the lower electrode plate 11 and insulation between the metal shell and the upper electrode plate. The insulation between the metal shell and the lower electrode plate and the insulation between the metal shell and the upper electrode plate are securely maintained in the case that the resin constituting the resin molded body is filled in the cylindrical space between the metal shell and the stacked components ranging from the lower insulating plate to the weight through a flow passage provided in the weight.
However, in the case that the groove section is provided in the metal shell and the stopper ring is crimped onto the groove section so as to be fixed to the cylindrical section, the metal shell and the stopper ring remaining in close contact with each other because the stopper ring is hardly deformed. In that case, the resin substantially flows only through the clearance between the insulating plates and the weight. As a result, the cylindrical space between the metal shell and the stacked components ranging from the lower insulating plate to the weight is hardly filled with the resin, whereby a problem arises in that it is difficult to maintain the insulation between the metal shell and the lower insulating plate and the insulation between the metal shell and the upper insulating plate.